Wait until players present their deck to their opponent before grabbing them.

Check for patterns in the cards order.

Sort the deck.

Compare with the deck list.

Check for marked cards/sleeves (it's usually easier to spot patterns when the deck is sorted)

Shuffle twice or thrice before giving the players their deck back

Note : If you want to check for controlled shuffling, you should wait after players have shuffled their opponent's deck before collecting the decks.
It may also be a good idea to notice how a player cut his own deck after his opponent shuffled it (the way he looks at his deck before cutting it, the way he places his deck on the playing area, etc.).

Gaining time
As part of the organization team, judges should try to have the event go as quickly and as smoothly as possible. Time can be gained by :

At the end of each round, make sure that every player has heard that the time was called and is aware that he should keep on playing at a normal pace.

Between rounds, being ready to post the pairings as soon as they are out of the printer can spare several minutes, especially if you have cut the tape in advance.

When dealing with players, the faster you deal with a players' call, the less extra time you'll give. You will also be available to deal with other problems faster.(note that there is a difference between solving a problem fast and getting rid of it. Being fair and true remains your main priority)

Note : Even though time is a real concern, you should never run. It doesn't look professional and doesn't help you to finish the day in a good shape.

Collecting result entry slips
Try to spare your legs and wait until you have a bunch of slips before going back to the computer (except at the end of the round when the scorekeeper is processing the data).

Always ask for confirmation from both players (especially the looser). Make sure that they understood your question and didn't give an automatic "yes" answer.

Double check for drops.

Sign with your full name or anything that can clearly identify you even to someone that doesn't know you (nickname or initials are not sufficient)

Dealing with player's call

First, check the clock in order to know how much time the ruling took.

Get both players' stories. If they disagree, you can get each version separately. Always understand completely what's going on before calling the head judge, even though the players want his final ruling, as he will surely ask you for facts on the way to the players.

If you have any doubt (even the slightest), double check.

Don't be afraid to read the cards and take some time before giving your ruling.

Don't get emotional. Calm the players down and don't argue too much.

Try to explain your ruling rather than imposing it.

If you must adjudicate a penalty, write extra time and a visible sign on the face of the entry slip (usually next to the player's name) and write down the exact penalty on the back with a quick but clear explanation and your full distinctive name (no signature).

Be generous with extra time. Most of the time it won't affect the tournament and players will feel better.

Managing a draft
During a draft :

It's impossible to spot every problem. The most important thing is to demonstrate that you are attentive and reactive. A good presence should prevent most problems.

The main goal is to keep up with the other tables. Deal with problems quickly and precisely and do not let players argue too much.

Stop the draft only if you can't handle the problem by yourself (bad boosters...) or quickly enough (real mess...)

Keep your table quiet.

During deck construction :

You don't need to sign every player's mistake. It's different from a sealed deck with a pre registered list. Here, as long as their list is clearly understandable, it doesn't need a judge approval.

Try to keep the room as quiet as possible.

When you have enough product, putting land on each table is usually the best solution as it gives you work when you have time for it (at the beginning of deck construction). If you can't, try to split queues as much as possible rather than gather them. For example, it's better to have to separate spots - one to collect the deck list, the other to hand out lands.

Professionalism
Even though we are usually volunteers, we still need to be consistent, rigorous and professional.

Keep the room neat

Always look aware and available

Don't spend too much time chatting with your friends especially if they are engaged in the tournament.

Don't cluster with other judges for too long.

Avoid taking part in another judge's ruling. You can watch to give him feedback afterwards but you shouldn't interfere. If you think that he is making a mistake, talk to him apart of the players

Avoid sitting down unless you are specifically watching a game. If you want to rest - which you should from time to time - go to the judge room.

Catching cheaters
Telling the difference between an honest mistake, a bad coincidence, and actual cheating is really difficult. And that's a mistake we can't afford.
The best way to prove cheating is when the honest mistake or the bad coincidence repeats itself. It has to be spotted on the long term. Keeping track of warnings from one tournament to another helps but you can also spot it in a single event.
The best strategy to catch cheating is usually to do nothing. When you've spotted something weird, keep on watching. If you react right away, you'll be able to correct the mistake (which is usually fairer to the opponent) but you won't have enough proof to conclude there has been cheating. The player will obviously stop cheating right away or will be a lot more cautious.
If you really want to catch him, you have to keep on watching.
If such a case should occur, inform the head judge as it will be easier to confirm your theory with different judges aware of what is happening.

Give feedback
We all need to improve. Giving feedback is not always easy but it's the best way to improve the whole judging community.

Don't hesitate to share stories with your fellow judges.

Take notes about interesting cases to raise during judge meetings.

Directly go talk to a judge when you've noticed something unusual. You will either be able to correct him or learn from him if his decision was wiser.